Transfer process of photographic printing



Nov. 29, 1955 H. c. YUTZY ETAL 2,725,298

TRANSFER PROCESS OF PHOTOGRAPHIC PRINTING Filed May 3, 1952 Fig. 1

SUPPORT EMULSION UNHARDE/VED COLLOID com/mus was/17m; AGENT l4 SOLVENT DEVELOPMENT SILVER ORSILVERCOMPOUND IMAGE TRANSFERREDCOLLOIDSTRATUM SUPPORT 6 LAYER CONTAIN/N6 21 INSOLUBLE SULFITE B'IIIIIIIIIII'.

lliliiiig NUCL'EATING LAYER Henry C. Yai y lierberfflcowden INVENTORS United States PatentO TSFER PROCESS OF PHOTOGRAPHIC PRINTING Henry C. Yutzy and Herbert B. Cowden, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application May 3, 1952, SerialNo. 285,855 3 Claims. (CI. 95-88 This invention relates to photography and particularly to a transfer process of printing a photographic image.

Various methods of forming an image in an unsensitized sheet by transfer from an originally sensitive layer have been described in the literature. In application Serial No. 783,913, filed November 4, 1947, now Patent No. 2,596,754, E. C. Yackel has described a procedure.

according to which a photographic image formed in an unhardened gelatin layerby conventional processing is transferred to a dry absorbent receiving sheet by squeegeeing the print, after processing, into contact with the dry absorbent surface, then stripping the two apart after a short interval of Contact. In this process a stratum of the gelatin layer is adhered to the receiving surface and transferred leaving behind the remainder of the gelatin layer containing part of the image. Upon rewetting the gelatin layer successive transfers can be made. This method produces a negative transferred image if a positive is used to make the original exposure.

Processes involving solvent transfer methods have also been described in the literature, a review of these appearing in an article by Varden in the Photographic Society of America Journal, vol. 13, September 1947, page 551. These processes involve development of an exposed silver halide emulsion layer with a developing solution containing a solvent for silver halide. During or immediately following initial development the exposed emulsion layer is placed in contact with another layer, usually unsensitized, and the dissolved silver salts representing the positive image are then transported to the second layer and deposited as a positive image. This method gives a posi-' tive transferred image if a positive image is used for the original exposure.

We have now found that an image formed in the outer of two superposed strata by the solvent transfer method may be transferred to the receiving sheet by the method of Patent 2,596,754 and that several successive transfers may be made in this way to produce duplicate images. Our method involves in general the use as the sensitive material of a photographic element comprising a support having a silverhalide emulsion layer thereon and an unhardened colloid layer overcoated on the emulsion layer so that the colloid layer is outermost. The colloid layer has dispersed therein an agent for promoting image for-- mation, comprising physical development nuclei or a chemical precipitant for dissolved silver ions, so that the dissolved silver salts transported to the colloid layer from the silver halide emulsion layer during solvent development, are deposited and retained in a visible form in the colloid layer. The image thus obtained in the colloid layer may be transferred layer-wise to an absorbent support and successive transfers of the colloid layer containing the image may be made on successive absorbent supports to produce duplicate images.

In the drawing, Fig. 1 illustrates sectional views of the photographic elements at various stages in our preferred process, and

Fig. 2 is a sectional view of a modified form of the sensitive element used according to our invention.

The silver halide emulsion used in the sensitive element of our invention may be an ordinary unsensitized gelatinosilver halide emulsion, or an optically sensitized or chemically sensitized emulsion, in which the gelatin is substantially unhardened or hardened in such a way that it does not harden the colloid layer coated over it, as explained more fully hereinafter. The emulsion may contain a substantially non-diffusing developing agent of the tanning type as disclosed in Yackel application Serial No. 783,912, filed November 4, 1947, now Patent No. 2,592,368 or a non-tanning, substantially non-diffusing developing agent as described in application Serial No. 267,447, filed January 21, 1952, by Yutzy and Yackel.

The colloid layer coated over the emulsion layer is a layer of water-susceptible or water-permeable colloid, such as gelatin or polyvinyl alcohol, containing an agent promoting image formation and capable of yielding with silver ion a dark-color silver substance, when the dissolved silver salts from the emulsion layer come in contact with it. This agentin the colloid layer may comprise either physical development nuclei or a chemical precipitant for dissolved silverions, the following being suitable agents:

' Colloidal silver The developing solution may be the usual and customary type of photographic developing solution containing hydroquinone, N-methyl-p-aminophenol sulfate, p-phenylene diamine, etc., or any mixture of these, as the developing agent and containing the usual ingredients such as alkali, potassium bromide and sodium sulfite. If the developing agent is incorporated in the emulsion layer the solution used to effect development may be a simple alkaline solution such as a sodium carbonate or sodium hydroxide solution. The developing solution must also contain a silver halide solvent such as sodium thiosulfate, sodium sulfite, ammonium hydroxide, ammonium sulfate, ammonium nitrate, ammonium chloride or a thiocyanate of an alkali metal. If the silver halide solvent is contained in the sensitive element as shown in'Examples 3 and 4 hereinafter, the developing solution need not of course contain a silver halide solvent. I

If a non-diffusing developing agent is to be used in the sensitive emulsion,'any of the following compounds will serve for this purpose:

3,4-dihydroxy-diphenyl 2,5 -dihydroxy-diphenyl 2,3-dihydroxy-diphenyl 5,6,7,8-tetrahydronaphthol hydraquinone 2-hydroxy-S-amino-diphenyl 3,4-diamino-diphenyl Dodecyl catechol Diamyl-hydroquinone Lauryl hydroquinone 3 our invention will be further illustrated by reference to the following specific examples.

Example 1 An ordinary photographic paper stock free from formaldehyde or other compound capable of hardening gelatin was coated with a high contrast contact speed gelatinosilver chloride emulsion substantially free of gelatin hardeners. On this photographic emulsion layer there was coated a layer of substantially unhardened gelatin containing colloidal zinc sulfide. This suspension was prepared as follows:

A 157 c me 23 cc. Fused Na2iS-'1 g'. in 1000 cc. H2O

B was poured into A room temperature with rapid stirring.- The mixture was quickly poured into 110 g. 20 percent gelatin (containing cc. 7.5 percent aqueous saponin) at 40 C. The whole was held at 40 C. for coating.

This composite element was exposed to a positive original and the silver halide emulsion layer developed to a negative in a developing solution of the following composition:

Water to 1 liter After development for approximately one minute there was formed in the nucleating layer a positive image. The sheet was removed from the developer solution, squeegeed to remove excess developer and pressed into contact with a sheet of absorbent paper, for example an ordinary bond typewriter paper. After a few seconds the photographic sheet was stripped from the receiving paper, which was found to carry a positive image representing a stratum of the total positive image formed in the over-coated nucleating layer.

The original photographic layer carrying the negative and the remainder of the nucleating layer with the positive image was rewet in the developer solution, squeegeed and rolled into contact with a second sheet of receiving paper, then stripped as before leaving another portion of the image on the second receiving sheet. This operation could be repeated several times.

The incorporation of from 1 to 20 per cent of urea in the developing bath to increase the softness of the gelatin image was found to be advantageous.

Example 2 An ordinary photographio paper stock was coated with a high contrast contact speed gelatino-silver chloride emulsion hardened with 4.9 cc. of 20 per cent formaldehyde solution per kilogram of emulsion. On this emulsion layer there was coated a layer of polyvinyl alcohol containing cadmium sulfide prepared as follows:

A. 46 grams of a 17% solution of polyvinyl alcohol in Water (which is a gel) was mixed with 234 cc. of water and melted at 80 C. The solution was cooled to 40 C. and mixed with 14.4 cc. of a NazS solution which had been made by dissolving 1 gram of fused NazS in sufficientwater to make 100 cc. of solution.

B. 45.6 cc. of CdCl2-2 /2H2O solution which had been made by dissolving 1 gram of the cadmium chloride in sufiicient water to make cc. of solution was prepared at room temperature.

B added to A with rapid stirring. Finally 10 cc. 7.5% aqueous saponin added. Dispersion held at 40 C. for coating. This composite element after exposure to a positive image and development in the developer of Example 1 was squeegeed to remove excess developer and rolled into contact with an absorbent receiving sheet. The positive image formed in the polyvinyl alcohol layer was transferred to the receiving support, yielding a direct positive image.

The advantage of this element is that conventional photographic emulsions with conventional hardening agents such as formaldehyde may be used. Such gelatin hardeners have little hardening action on polyvinyl alcohol so that the polyvinyl alcohol layer retains the proper physical characteristics for a transfer to the receiving sheet.

Example 3 A photographic paper support free from formaldehyde or other gelatin hardeners bearing instead of the usual baryta coat a similar layer made with barium sulfite instead of barium sulfate was coated with the emulsion layer of Example 1 containing 12 g. of 3,4-dihydroxy diphenyl per kilogram of emulsion and also the nucleating layer of Example 1. The nucleating layer could also be coated on a separate sheet and squeegeed into contact with the emulsion layer just prior to the development process. The barium sulfite layer was made as follows:

H2O (65 C.) 750 cc. BaCl2.H2O 213 g.

H20 (boiling) 1500 cc. NazSOs' g. (10% excess) G. NazCOaHzO 50 NaOH l5 Urea 100 Water to 1 liter The theory of development of this element is as follows: When the exposed silver halide layer is brought into contact with the developing solution, development is initiated and carried well toward completion as the developing solution penetrates the colloid layer, the concentrations of silver halide solvent no higher than those used in conventional development. This allows development to a negative image before appreciable solution and subsequent transfer of silver halide to the nucleating layer via silver halide solvent occurs. As the developing solution penetrates through the emulsion to the undercoated barium sulfite layer the carbonate and hydroxyl ions in the developing solution react with the barium sulfite to produce barium carbonate and barium hydroxide, thus liberating the sulfite ion as the alkali salts and these difiuse back through the emulsion layer to the nucleating layer to efiect the usual silver halide transfer.

It is also desirable in this case to add some neutral sulfate such as sodium sulfate to the developer since barium sulfate is considerably less soluble than the carbonate, hydroxide or sulfite and will effect a more nearly complete conversion of the barium sulfite to sulfate, thus liberating the soluble sulfite more efficiently.

Other solvent systems may be substituted for the barium sulfite such as calcium or strontium sulfite. Other examples of solvents are slightly soluble or non-wandering ammonium salts or amines. Long-chain amines may be included in the undercoat by coating high molecular resins in the layer as complexes with the amines, the complexes being broken up by the action of the alkali in the developer.

A separate receiving sheet bearing the nucleating layer may be used in conjunction with a conventional silver halide paper, by incorporating the insoluble or nonwandering solvent in the nucleating layer or under the nucleating layer on the receiving sheet. It will be apparent also that the silver halide emulsion may contain a substantially non-diffusing developing agent as de scribed in Example 3, the chemical energy required for formation of the positive image being obtained from suitable reagents in a second layer either overcoated on the emulsion layer or coated on a second transfer sheet.

In the process of Example 1 in which both emulsion and nucleating layer were unhardened it has been found that there is some tendency for the fracture to occur at the paper base during transfer to the receiving sheet, resulting in unwanted transfer of all of the layers. This can be prevented by incorporating in the baryta layer or in a layer beneath the sensitive emulsion layer a completely exposed silver halide emulsion having therein an insoluble tanning developing agent. During development the completely exposed or fogged bottom layer is rapidly de veloped and tanned at the same time thus hardening the bottom layer and causing it to adhere more strongly to the paper support. This layer may contain the usual baryta or it may contain barium sulfite as described in Example 3. The black density developed in the barium sulfite layer does not affect the transfer results. The following example illustrates a coating made in this way.

Example 4 A paper support was coated with a suspension of barium sulfite, silver chloride emulsion, and 4-phenyl catechol as a tanning developing agent. This layer was thoroughly flashed to white light before subsequentcoating. Over this layer there was coated a gelatino-silver chloride emulsion also containing 4-phenyl catechol. Over the emulsion there was coated a gelatin layer containing zinc sulfide.

After exposure to an image this material was developed for two to three minutes in an alkaline solution. This caused (1) complete development of the silver in the bottom layer accompanied by tanning of the gelatin in the layer, (2) development of the negative image in the photosensitive layer and solution of the undeveloped silver halide in this layer by the sulfite ion from the bottom layer and (3) diffusion of the silver sulfite complex to the top layer where the silver was deposited as silver sulfide in the form of a positive image. When successive fractions of the top layer were transferred to a receiving support there was little if any tendency for all of the layers to transfer at once.

Our invention will now be described by reference to the accompanying drawing. As shown in Fig. 1 a support has coated thereon a silver halide emulsion layer 11 having exposed portions 12 and unexposed portions 13, an unhardened colloid layer 14 containing a nucleating agent which is coated over the emulsion layer 11. Upon solvent development of this material a silver image 15 is formed in layer 11 and a silver or silver compound image 16 is formed in the nucleating layer by solvent transfer. When this element is rolled into contact with a receiving sheet 17 a portion 18 of the nucleating layer carrying the image is transferred to the sheet 17 as shown in the final stage of Fig. 1.

Fig. 2 illustrates the modification of our material in which a support 20 is coated with a layer 21 containing an insoluble sulfite, an emulsion layer 22 and a nucleating layer 23.

Where we refer to a substantially unhardened gelatin emulsion layer we mean a layer that is not harder than would be the case with gelatin containing 0.25 ounce of formaldehyde (40 per cent, diluted 1 to 3 with water) per pound of gelatin when freshly coated, or 0.1 ounce of the forlnaldehyde solution per pound of gelatin for a sample aged 3 to 6 months.

Where we refer to transferring a continuous stratum of the emulsion layer we mean that a thin layer of the total surface area of the photographic element is carried off onto the receiving support.

It will be understood that the modifications and equivalents included herein are by way of example only and that our invention is to be taken as limited only by the scope of the appended claims.

We claim:

1. The method of photographic reproduction which comprises exposing to a subject a photographic element comprising a support having thereon a silver halide emulsion layer and an unhardened colloid layer on said emulsion layer, said colloid layer having dispersed therein an agent for promoting image formation, selected from the class consisting of physical development nuclei and chemical precipitants for dissolved silver ions, developing said exposed emulsion layer with a silver halide developing agent in the presence of a silver halide solvent to form a negative image in said emulsion layer and a positive image in said colloid layer, and transferring a continuous stratum of said colloid layer to an absorbent support.

2. The method of photographic reproduction which comprises exposing to a subject a photographic element comprising a support having thereon a silver halide emulsion layer and an unhardened gelatin layer on said emulsion layer, said gelatin layer having dispersed therein an agent for promoting image formation, selected from the class consisting of physical development nuclei and chemical precipitants for dissolved silver ions, develop ing said exposed emulsion layer with a silver halide developing agent in the presence of a silver halide solvent to form a negative image in said emulsion layer and a positive image in said gelatin layer, and transferring a continuous stratum of said gelatin layer bearing said positive image, to an absorbent support.

3. The method of photographic reproduction which comprises exposing to a subject a photographic element comprising a support having thereon an unhardened gelatino-silver halide emulsion layer and on said emulsion layer an unhardened gelatin layer having cadmium sulfide dispersed therein, developing said exposed emulsion layer with hydroquinone and N-methyl-p-aminophenol sulfate in the presence of sodium thiosulfate to form a negative silver image in said emulsion layer and a positive nucleated silver image in said gelatin layer, and transferring a continuous stratum of said gelatin layer bearing said positive image, to an absorbent support.

References Cited in the file of this patent UNITED STATES PATENTS 2,500,421 Land Mar. 14, 1950 2,543,181 Land Feb. 27, 1951 2,565,377 Land Aug. 21, 1951 2,596,754 Yackel May 13, 1952 2,647,056 Land July 28,1953

FOREIGN PATENTS 59,365 Netherlands Apr. 17, 1947 

1. THE METHOD OF PHOTOGRAPHIC REPRODUCTION WHICH COMPRISES EXPOSING TO A SUBJECT A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT HAVING THEREON A SILVER HALIDE EMULSION LAYER AND AN UNHARDENED COLLOID LAYER ON SAID EMULSION LAYER, SAID COLLOID LAYER HAVING DISPERSED THEREIN AN AGENT FOR PROMOTING IMAGE FORMATION, SELECTED FROM THE CLASS CONSISTING OF PHYSICAL DEVELOPMENT NUCLEI AND CHEMICAL PRECIPITANTS FOR DISSOLVING SILVER IONS, DEVELOPING SAID EXPOSURE EMULSION LAYER WITH A SILVER HALIDE DEVELOPING AGENT IN THE PRESENCE OF A SILVER HALIDE SOLVENT TO FORM A NEGATIVE IMAGE IN SAID EMULSION LAYER AND A POSITIVE IMAGE IN SAID COLLOIDAL LAYER, AND TRANSFERRING A CONTINUOUS STRATUM OF SAID COLLOIDAL LAYER TO AN ABSORBENT SUPPORT. 